372 TECTONICS/Mid-Ocean Ridges sites, and improvements in mathematical modelling techniques will stimulate the science over the next decade Finally, we believe that analysis of seafloor hydrothermal activity over geological time, and attempts to discern the importance of hydrothermal activity elsewhere in the solar system will emerge as an important endeavour Such studies are necessary to understand the links between hydrothermal activity and life In terrestrial systems continued exploitation as an energy resource will be important Moreover, climatically induced precipitation changes, because of the link to hydrothermal recharge, may alter warm spring and geyser behaviour Utilization of hydrothermal activity as a climate monitor has yet to receive attention See Also Geysers and Hot Springs Igneous Processes Mining Geology: Hydrothermal Ores; Magmatic Ores Origin of Life Plate Tectonics Tectonics: Faults Further Reading Anderson RN, Langseth MG Jr, and Sclater JG (1977) The mechanisms of heat transfer through the floor of the Indian Ocean Journal of Geophysical Research 82: 3391 3409 Bischoff JL and Pitzer KS (1989) Liquid vapor relations for the system NACL H2O: Summary of the P T x surface from 300 to 500 C American Journal of Science 289: 217 248 Bischoff JL and Rosenbauer RJ (1984) The critical point and two phase boundary of seawater, 200 500 C Earth and Planetary Science Letters 68: 172 180 Craig H (1961) Standard for reporting concentrations of deuterium and oxygen 18 in natural waters Science 133: 1833 1834 Elder J (1981) Geothermal Systems San Diego, CA: Aca demic Press Elderfield H and Schultz A (1996) Mid ocean ridge hydro thermal fluxes and the chemical composition of the ocean Annual Reviews of Earth and Planetary Science 24: 191 224 Germanovich LN, Lowell RP, and Astakhov DK (2000) Stress dependent permeability and the formation of sea floor event plumes Journal of Geophysical Research 105: 8341 8354 Humphris SE, Zierenberg RA, Mullineaux LS, and Thompson RE (eds.) (1995) Seafloor Hydrothermal Systems: Physical, Chemical, and Biological Interactions, AGU Geophysical Monograph 91 Washington, DC: American Geophysical Union Kelley DS, Baross JA, and Delaney JR (2002) Volcanoes, fluids and life at mid ocean ridge spreading centers Annual Review of Earth and Planetary Science 30: 385 491 Kruger P and Otte C (eds.) (1973) Geothermal Energy Stanford, CA: Stanford University Press Lowell RP (1991) Modeling continental and submarine hydrothermal systems Reviews of Geophysics 29: 457 476 Lowell RP (1992) Hydrothermal systems In: Nierenburg WA (ed.) Encyclopedia of Earth System Science, vol 2, pp 547 557 San Diego, CA: Academic Press Lowell RP, Rona PA, and Von Herzen RP (1995) Seafloor hydrothermal systems Journal of Geophysical Research 100: 327 352 Rona PA (1988) Hydrothermal mineralization at oceanic ridges Canadian Mineralogist 26: 431 465 Sclater JG, Jaupart C, and Galson D (1980) The heat flow through oceanic and continental crust and the heat loss of the Earth Review of Geophysics 18: 269 311 Von Damm KL (1995) Controls on the chemistry and tem poral variability of seafloor hydrothermal fluids In: Humphris SE, Zierenberg RA, Mullineaux LS, and Thompson RE (eds.) Seafloor Hydrothermal Systems: Physical, Chemical, and Biological Interactions, AGU Geophysical Monograph 91, pp 222 247 Washington, DC: American Geophysical Union White DE (1973) Characteristics of geothermal resources In: Kruger P and Otte C (eds.) Geothermal Energy Stan ford, CA: Stanford University Press Mid-Ocean Ridges K C Macdonald, University of California–Santa Barbara, Santa Barbara, CA, USA ß 2005, Elsevier Ltd All Rights Reserved Introduction The mid-ocean ridge system is the largest mountain chain and the most active system of volcanoes in the solar system In plate-tectonic theory, the ridge is located between plates of the Earth’s rigid outer shell that are separating at speeds of approximately 10–170 mm year (up to 220 mm year in the past) The ascent of molten rock from deep within the Earth (ca 30–60 km) to fill the void between the plates creates new seafloor and a volcanically active ridge This ridge system wraps around the globe like the seam of a baseball and is approximately 70 000 km long (including the lengths of ridge offsets, such